Transistors are dominant and important devices in fabricating integrated circuits. They may be used for amplifying, switching, and detecting signals and typically contain at least two rectifying junctions connected to metallic contacts. Characteristically transistors operate so the current between one pair of terminals controls the current between the other pair, one terminal being common to output and input. The operation and fabrication of many types of transistors are well known and described in numerous references including S. M. Sze, SEMICONDUCTOR DEVICES (1985), which is incorporated herein by reference. Generally, transistors are made from electrically-conducting materials, such as metals and substrates doped with phosphorous, arsenic, or boron to form p and n-type carrier regions, and they are electronically operated, i.e., they operate based on the electrical properties of the materials.
A photonic band-gap (PBG) material has the property of preventing electromagnetic radiation having some discrete wavelength or range of wavelengths from propagating within the material. The photonic band-gap has been formed by creating a periodicity in a material's dielectric properties in two or three dimensions. This may be accomplished with use of an array of holes or cavities in layers of dielectric materials so there is a two or three dimensional change in the dielectric properties of the materials.
For example, FIG. 1 shows a perspective view of a prior art PBG material that is periodic in two dimensions, that is, it has a repeated two-dimensional change in dielectric composition. The PBG material 10 is comprised of a first material 11 having a first dielectric composition or permittivity .epsilon..sub.1 in which is disposed a plurality of cylindrical elements 12a, 12b, 12c, etc., each of which is comprised of a second material having a second dielectric composition or permittivity .epsilon..sub.2 relative to the first material. The cylindrical elements may be filled with gasses or fluids or they may be left hollow to define voids. Periodicity is established along the x-z plane due to differences in the dielectric properties of the materials such that electromagnetic energy within the range of a band-gap and polarized along the longitudinal axes of the elements 12a, 12b, 12c, etc. is substantially prevented from propagating through the material 10. The material is most effective for blocking electromagnetic radiation propagating along any incident angle of the x-z plane.
Many PBG devices have operated in the microwave region of the electromagnetic spectrum and thus have had limited utility. New materials and processes for use in forming the photonic band-gap material are being developed so that they may operate across a wider range of wavelengths to expand potential uses for the devices. For example, U.S. Pat. No. 5,385,114 and U.S. Pat. No., 5,688,319 issued Jan. 31, 1995 and Nov. 18, 1997, respectively, both to Milstein et al. and titled "Photonic Band-Gap Materials and Method of Preparation Thereof" (both incorporated herein by reference), describe use of a sapphire band-gap material in single crystal form which is designed to expand the range of wavelengths controlled from the millimeter or microwave region to the ultraviolet region. An antenna using PBG materials is disclosed in U.S. Pat. No. 5,689,275 issued Nov. 18, 1997, to Moore et al. "Electromagnetic Antenna Transmission Line Utilizing Photonic Band-Gap Material" ("Moore").
Another difficulty relating to PBG devices, which limits the potential uses for these devices, involves tuning them to operate at specific wavelengths. For example, in Moore, dielectric material is used to fabricate the photonic band-gap antenna, and to vary the frequency at which the photonic band-gap appears, cooling liquid is circulated within the periodically placed voids. The Milstein '114 and '319 patents describe that PBG devices may be tuned to operate within distinct portions of the spectrum by modifying the physical dimensions of the material forming the device, by modifying the voids, by infiltrating liquid or solid materials in the voids, or by applying mechanical pressure on the surface of the material to thereby modify the relative dimensions of the voids and solid portions (e.g., altering the dimensions of the cylindrical rods). Milstein '114 and '319 teach that PBG devices may be tuned by deliberating changing the device dimensions, e.g., with electrostriction or magnetostriction. However, there are limits to the extent of tuning that may be performed with these approaches, because changing the dimensions in a way sufficient to achieve more expansive tuning could threaten the structural integrity of the device.
Those concerned with semiconductor devices and technologies continually search for new components and designs, e.g., devices that are tunable, operable at higher speeds, use less power, and have less complicated parts. The instant invention provides a photonic band-gap device that may be utilized as a transistor to offer advantages over electronically-operated transistors as it operates over a wide range of wavelengths and is tunable with the application of light. The transistor is particularly useful for forming arrays of devices to perform computational functions.